The initiation factors required for the translation of globin mRNA have been prepared in pure form except for eIF-4B which has been prepared in a form that appears to be approximately 70% pure. Attempts to further fractionate the one crude component (a mixture of aminoacyl-tRNA synthetases) used in the translation of globin mRNA suggest that additional components may stimulate the synthesis of a and b globin chains. Radiolabeled initiation factors have been prepared by reductive alkylation using (14C) HCHO and NaBH4. The use of radiolabeled initiation factors, AUG, (3H)Met-tRNAf, 40S subunits, 60S subunits, GTP and various GTP analogs have allowed us to define nore precisely the sequence of events in AUG directed 80S initiation complex formation. Based upon the observations that suggest that the hemin controlled repressor (HCR) is a protein kinase, several protein kinases have been isolated from rabbit reticulocytes. These protein kinases have been shown to differentially phosphorylate eIF-2, eIF-3, eIF-4B, and eIF-5. One of the protein kinase preparations appears to have properties similar to HCR as judged by its ability to shut off the initiation of protein synthesis. BIBLIOGRAPHIC REFERENCES:Anderson, W.F., Bosch, L., Cohn, W.E., Lodish, H., Merrick, W.C., Weissbach, H., Wittman, H.G. and Wool, I.G.: International symposium on protein synthesis. FEBS Lett. 76: 1-10, 1977. Safer, B., Peterson, D., and Merrick, W.C.: The effect of hemin controlled repressor on initiation factor functions during sequential formation of the 80S initiation complex. In: Proceedings of the International Symposium on Translation of Synthetic and Natural Polynucleotides . Poznan, Poland, 1977, in press.